Comparison of the International Federation of Clinical Chemistry and Japan Diabetes Society reference methods for conversion to the National Glycohemoglobin Standardization Program values

The national programmes for the harmonization of haemoglobin A1c measurement in the US and Japan are based on differently designated comparison methods. The future basis for international standardization is expected to be the reference system developed by the International Federation of Clinical Chemistry (IFCC) Working Group on haemoglobin A1c Standardization. The aim of the present study is to compare the relationship between the IFCC reference method (RM) and Japanese Diabetes Society (JDS) RM used for the conversion to the National Glycohemoglobin Standardization Program (NGSP) values. Three different method-comparison studies were performed. All blood samples were measured at the National Cerebral and Cardiovascular Centers (Lipid Reference Laboratories) that serve as Level 1 reference laboratories of the NGSP Network. Regression equations were calculated for the IFCC RM and JDS RM for the conversion to NGSP values. Differences were found between the haemoglobin A1c values of the IFCC RM and those of JDS. However, in all cases, the relationships of the IFCC RM and JDS RM were linear and commutable. The relationship is described by the following regression equations: NGSP-HbA1c？=？0.915(IFCC-HbA1c)？+？2.15% (r2？=？0.998); JDS/JSCC-HbA1c？=？0.927(IFCC-HbA1c)？+？1.73% (r2？=？0.997). There is a firm and reproducible link between the IFCC and JDS-HbA1c values. However, the values calibrated by JDS RM were consistently and significantly higher than the IFCC values (0.1–0.2%) when used for conversion to the NGSP values